Development of a diagnostic question cluster and post-assessment of college student understanding about population dynamics Miranda A. Kearney and Nancy E. Stamp Biological Sciences, Binghamton University - State University of New York, Binghamton, NY Pre-assessment Post-assessment Iteration #1 (N=271 introductory biology students) Iteration #2 (N=24) After a lecture and reading but prior to a class activity on the subject of population dynamics, students were asked questions based on data from Gause ’ s Paramecium experiments. Initially, we used a common textbook representation of that data (Fig. 1). This classic set of experiments nicely illustrates: 1.Phases in population growth (exponential, then effects of limiting factors resulting in slowed growth that eventually plateaus) 2.Support for Lotka-Volterra logistic model 3.Different species have different carrying capacities (K) 4.An example of intraspecific and interspecific competition We provided more detail about the Gause experiments and asked questions only about Figure 1C. We added another question that included a different graph with actual data points. We asked which figure was a better illustration of Gause ’ s results and why. After a class activity, we administered a post-assessment to determine if the activity helped students overcome misconceptions about population dynamics. We used estimates of linked prey and predator populations for the following reasons: 1.This data set is used in many textbooks as an example of cycles in population size that can be readily explained 2.The snowshoe hare is a critical species in boreal ecosystems; its loss would result in loss of predator species and a significantly altered plant community (Krebs et al. 2001) 3.Study of the hare-lynx relationship has helped ecologists understand how time lags in both direct and indirect effects predation contribute to population cycles Sample Questions & Responses: A. How do you explain that these two species can coexist in a pond? 35% said: Two species cannot coexist because Fig. 1C shows that they are unable to live in the same environment 20% - Ponds have more space 17% - Ponds are larger and contain multiple exploitable niches 13% - There is more food available in the pond 9% - Pond have more food and are larger B. If daily samples were taken from a pond over a 2.5-week period, what do you think the population growth patterns would look like? Figure 1: Gause’s Experiments Figure 2: From Gause’s The Struggle for Existence (1934) Iteration #1 (N=274) Best Student Description: “This figure is a better illustration of Gause’s results because it is logical that both species would show a decline in population density when in competition with one another. Even if P. aurelia vastly out-competes P. caudatum as long as P. caudatum has not gone extinct, it should still be showing reduced numbers from those of the species by itself.” 92% Preferred graph with data points (fig. 2) 8% Preferred smooth graph (fig. 1) Figure 3: Hare and lynx data from historic pelt records of the Hudson ’ s Bay Company Sample Questions & Responses: A.What is the carrying capacity for the hare population? For the lynx population? 93% said: It is the maximum peak on the graph (i. e., approx. 150,000 hares and 80,000 lynx) 4% - It is an average across the 100-year time scale of the graph (i.e., approx.70,000 hare and 40,000 lynx) Only one student responded that it changed with resources B.What determines the carrying capacity for the hare population? 28% said: Predation (or more specifically the number of lynx) 28% - Other or blank (many said carrying capacity was determined by the “ peak of the graph ” ) 22% - Available food or resources 18% - Combination of available resources and number of lynx 4% - Space C.What causes the cyclical pattern seen in the graph? 47% said: Prey population increases causing the predator population to increase. This causes the prey population to decrease. Soon after, the predator population also begins to decrease. 24% - The Lotka-Volterra Model 22% - Other or blank 7% - Described the lynx and hare interaction in detail addressing food supply limits and population dynamics Textbook analysis 66% of 12 recent textbooks (5 introductory biology and 7 ecology) used Gause’s Paramecium experiments to illustrate logistic growth But only one used the graphs well 92% used hare-lynx pelt data Only 58% used subsequent research to explore causes of the cycles Definitions of carrying capacity varied within and among textbooks Conclusion Typical presentations of concepts, data and application fall far short of objective.